In a typical cellular radio system, wireless terminals communicate via a radio access network, RAN, to one or more core networks. The wireless terminals can be mobile stations or user equipment units, UE, such as portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network, e.g., mobile telephones and laptops with wireless capability.
The RAN covers a geographical area which is divided into cell areas, with each cell area or group of cell areas being served by a radio access node. A cell is a geographical area where radio coverage is provided by equipment at the radio access node. Each cell is identified by an identity within the local radio area. The radio access nodes communicate over the air interface with the UE within the cells served by the node.
The Universal Mobile Telecommunications System, UMTS, is a third generation mobile communication system, which evolved from the Global System for Mobile Communications, GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access, WCDMA, access technology. UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units, UEs. The Third Generation Partnership Project, 3 GPP, has undertaken to evolve further the UTRAN and GSM based radio access network technologies. Specifications for the Evolved Universal Terrestrial Radio Access Network, E-UTRAN, are ongoing within the 3GPP. Another name used for E-UTRAN is the Long Term Evolution, LTE, Radio Access Network, RAN.
Long Term Evolution RAN is a 3GPP radio access technology wherein a flat architecture is used with a singled type of nodes connected directly to a core network. The LTE RAN comprises evolved radio access nodes, e.g., evolved NodeBs or eNodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the user equipment. A common implementation of an eNodeB is a three-sector site, where the eNodeB includes equipment for handling transmissions in three cells. However, other implementations can be found as well. The eNodeB hosts functions for radio resource management, mobility management and user plane functions, among others. The eNodeB is connected to the core-network by means of the S1 interface.
Within the LTE RAN there may be occurrences of cell outage, i.e., cells that due to hardware or software engineering faults suffer from loss of call processing. The lack of processing of traffic in a cell causes an inability in the node to process incoming calls or handle data for ongoing calls. A cell outage is a state when the cell cannot handle any of the offered traffic in the area covered by the cell. There are multiple reasons for a cell outage, e.g., hardware and software failures (radio board failure, channel processing implementation error etc), external failures such as power supply or network connectivity failures, or even erroneous configuration. When a cell is in an outage state, the cell cannot support any users in its vicinity. For the operators of wireless access networks this is an undesirable consequence as potential revenue is missed from the unsupported traffic and also customer satisfaction is damaged. It is important to be able to detect the state of cell outage promptly to be able mitigate the effect of the cell outage and to redirect the users to other cells within the radio access node or to other radio access nodes.
A cell outage, i.e. one or more malfunctioning radio cells of a base station, e.g. a LTE eNB, may be detected by the base station associated with the affected radio cell by internal surveillance of processing boards and RF components of the base station. Some cell outage cases may also be detected by Operations Support System (OSS) functions through performance counters and/or alarms. By investigating a portion of the traffic related counters and their recent history, one can detect when a cell might have gone into a state of cell outage, a so called “Sleepy Cell”. However, with the presently available solutions, detection of cell outage may be delayed for hours or even days. It is often through long term performance analysis and subscriber complaints that the outages are detected. Currently, discovery and identification of some errors may involve manual analysis and may require unplanned site visits, which makes cell outage detection a costly task.
There is a need for improved solutions for determining a cell state in a radio access network.